In the development of containers for the retention of liquid under pressure, for example carbonated beverages, beer and the like, it is desirable to provide the container with a "pressure bottom" configuration. Such bottoms are generally convex in configuration, although "domed" or concave configurations also are utilized. These bottom configurations generally avoid the sharp contour transition portions located at the "heels" of a conventional flat-bottom beverage container, and, as a result, enhanced bottom strength in the container is obtained.
This strength advantage is obtained in several ways. First, the design itself is simply better adapted to serve as a pressure vessel. Secondly, it is not necessary to move the plastic material, during blowing, into the sharp bottom areas or "heels" of the container, with the inevitable thinning of the plastic material at the heels. Additionally, better wall distribution generally is obtained throughout the entire container, not only at the bottom.
Containers having arcuate pressure bottom configurations suffer from one prime disadvantage, i.e. the convex bottom simply will not allow the container to stand upright during filling, shipping, display or use. This problem has been solved in the past by utilizing separately formed skirts or angular support walls which are adhered to the bottom to provide a support base. The cost of assembly, the utilization of disparate container and base materials, and the necessity of adhesive application all have caused difficulties in the utilization of this type of container.